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AK: Make Weakable non-atomic
Let's not punish single-threaded workloads with the performance cost of atomic weakables. The kernel keeps using LockWeakable.
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53c0038d2c
Notes:
sideshowbarker
2024-07-17 20:58:35 +09:00
Author: https://github.com/awesomekling Commit: https://github.com/SerenityOS/serenity/commit/53c0038d2c
@ -7,11 +7,9 @@
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#pragma once
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#include <AK/Assertions.h>
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#include <AK/Atomic.h>
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#include <AK/RefCounted.h>
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#include <AK/RefPtr.h>
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#include <AK/StdLibExtras.h>
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#include <sched.h>
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namespace AK {
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@ -31,50 +29,18 @@ public:
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RefPtr<T> strong_ref() const
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requires(IsBaseOf<RefCountedBase, T>)
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{
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RefPtr<T> ref;
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{
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if (!(m_consumers.fetch_add(1u << 1, AK::MemoryOrder::memory_order_acquire) & 1u)) {
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T* ptr = (T*)m_ptr.load(AK::MemoryOrder::memory_order_acquire);
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if (ptr && ptr->try_ref())
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ref = adopt_ref(*ptr);
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}
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m_consumers.fetch_sub(1u << 1, AK::MemoryOrder::memory_order_release);
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}
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return ref;
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return static_cast<T*>(m_ptr);
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}
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template<typename T>
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T* unsafe_ptr() const
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{
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if (m_consumers.load(AK::MemoryOrder::memory_order_relaxed) & 1u)
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return nullptr;
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// NOTE: This may return a non-null pointer even if revocation
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// has been triggered as there is a possible race! But it's "unsafe"
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// anyway because we return a raw pointer without ensuring a
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// reference...
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return (T*)m_ptr.load(AK::MemoryOrder::memory_order_acquire);
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return static_cast<T*>(m_ptr);
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}
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bool is_null() const
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{
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return unsafe_ptr<void>() == nullptr;
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}
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bool is_null() const { return m_ptr == nullptr; }
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void revoke()
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{
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auto current_consumers = m_consumers.fetch_or(1u, AK::MemoryOrder::memory_order_relaxed);
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VERIFY(!(current_consumers & 1u));
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// We flagged revocation, now wait until everyone trying to obtain
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// a strong reference is done
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while (current_consumers > 0) {
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sched_yield();
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current_consumers = m_consumers.load(AK::MemoryOrder::memory_order_acquire) & ~1u;
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}
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// No one is trying to use it (anymore)
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m_ptr.store(nullptr, AK::MemoryOrder::memory_order_release);
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}
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void revoke() { m_ptr = nullptr; }
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private:
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template<typename T>
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@ -82,8 +48,8 @@ private:
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: m_ptr(&weakable)
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{
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}
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mutable Atomic<void*> m_ptr;
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mutable Atomic<unsigned> m_consumers; // LSB indicates revocation in progress
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mutable void* m_ptr { nullptr };
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};
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template<typename T>
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